Amine-linked diglycosides: Synthesis facilitated by the enhanced reactivity of allylic electrophiles, and glycosidase inhibition assays

• Ian Cumpstey,
• Jens Frigell,
• Elias Pershagen,
• Tashfeen Akhtar,
• Elena Moreno-Clavijo,
• Inmaculada Robina,
• Dominic S. Alonzi and
• Terry D. Butters

Beilstein J. Org. Chem. 2011, 7, 1115–1123, doi:10.3762/bjoc.7.128

• , with m/z 734, consistent with the expected coupling products, i.e., the allylic amines. The fourth product had m/z 800, consistent with the carbamate structure 27. The determination of the regiochemistry of the unsaturated ring in 24 was complicated by long-range 1H–1H couplings and correlations in the

• COSY spectrum. It was difficult to distinguish between the C/H-2 and C/H-4 pairs of signals due to the presence of a cross-peak between 2-H and 5-H and the very low intensity of the cross-peaks between 1-H and both 2-H and 4-H, and between 4-H and 5-H. The regiochemistry was established by the presence

• ) [40][42][43], similar to the 2,3-unsaturated-4-amino compounds. Therefore, use of 13C C-1 chemical shift alone as a diagnostic tool for regiochemistry should be avoided. A further characteristic feature that can be used to distinguish 2-amino-3,4-unsaturated-α-threo configured compounds from their α

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• . Gung and co-workers developed a 3,3-rearrangement/transannular [4 + 3] cycloaddition reaction (Scheme 40) in the presence of either a Au(I) or Au(III) catalyst [109]. In these reactions, the regiochemistry of the product 223 is controlled by the position of the acetoxy group in the starting material

• 222, while the stereochemistry of the reaction depends on the ring size. In some gold(I)-catalyzed cycloaddition reactions, regiochemistry of the product is controlled by the ligand [100][101]. For example, the triphenylphosphinegold(I)-catalyzed reaction of allene–diene 224 provided a 2:1 mixture of

Alkene selenenylation: A comprehensive analysis of relative reactivities, stereochemistry and asymmetric induction, and their comparisons with sulfenylation

• Vadim A. Soloshonok and
• Donna J. Nelson

Beilstein J. Org. Chem. 2011, 7, 744–758, doi:10.3762/bjoc.7.85

• the degree of substitution on C=C or upon substituent electronic effects. Electronic and steric effects influencing asymmetric induction, stereochemistry, regiochemistry, and relative reactivities in the addition of PhSeOTf to alkenes are compared and contrasted with those of PhSCl. Keywords: alkene

• the intermediate seleniranium ion can be efficiently controlled [71]. It is assumed that the first reversible [69] step of the reaction determines the absolute configuration of the products and the second, rate-determining step, controls the regiochemistry [15][16][17][18][27][28][29][30][31][32][33

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

• Sami F. Tlais and
• Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

• of common reaction conditions. Conversely, the use of alkynes in the synthesis of spiroketals introduces regiochemistry concerns as to which of the two alkyne carbons becomes the spiroketal carbon, and the kinetic stability of alkynes must be overcome when alkyne reactivity is desired. As an off

• consensus option has emerged. Utimoto studied the palladium-catalyzed cycloisomerization [8] and reported that a range of spiroketals are available in excellent yield (e.g., Scheme 3, Reaction 1). However, regiochemistry is sometimes difficult to control, and De Brabander later found variability in reaction

• dehydration to furan 10. The use of alkyne-diol cycloisomerization instead of ketone-diol cyclocondensation is important for the potential success of this approach, since β-alkoxy ketone 9 (Scheme 4, inset) would be more prone to undesired elimination than homopropargyl ether 6. We addressed regiochemistry by

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• regiochemistry of proton catalyzed addition of alcohols to enols or enol ethers has the opposite regiochemistry to that observed in the product [102]. Furthermore, an electron transfer intermediate was ruled out, as the reaction is not thermodynamically feasible according to the Weller equation. Therefore, he

Approaches towards the synthesis of 5-aminopyrazoles

• Ranjana Aggarwal,
• Vinod Kumar,
• Rajiv Kumar and
• Shiv P. Singh

Beilstein J. Org. Chem. 2011, 7, 179–197, doi:10.3762/bjoc.7.25

• that reaction is initiated on the vinyl ether (vinylamine) group of 74a/b to give 5-aminopyrazole-4-carbonitrile 76 through the intermediacy of 75 [59]. However, Elnagdi et al. [60] have reported that when ethyl hydrazinoacetate condenses with 74a or b, a change in regiochemistry occurs to yield 3

Palladium- and copper-mediated N-aryl bond formation reactions for the synthesis of biological active compounds

• Carolin Fischer and
• Burkhard Koenig

Beilstein J. Org. Chem. 2011, 7, 59–74, doi:10.3762/bjoc.7.10

• (Scheme 13). The method benefits from controlled regiochemistry and is applicable to various aliphatic and aromatic amines 58. Although the reaction scope was limited to 1-bromo-2-iodobenzenes 59, scale-up to multigram quantities was possible [65]. A key intermediate 64 of imatinib 61, a standard anti

Carbasugar analogues of galactofuranosides: α-O-linked derivatives

• Jens Frigell and
• Ian Cumpstey

Beilstein J. Org. Chem. 2010, 6, 1127–1131, doi:10.3762/bjoc.6.129

• the epoxide 4 by alcohol nucleophiles under Lewis acidic conditions as used in the diastereomeric series [9]. With excess ethanol (10 equiv), we obtained the C1 ethyl ether 8 as the major product (90%) along with a small amount (4%) of the regioisomer (Scheme 2). The regiochemistry was proved by

En route to photoaffinity labeling of the bacterial lectin FimH

• Thisbe K. Lindhorst,
• Michaela Märten,
• Andreas Fuchs and
• Stefan D. Knight

Beilstein J. Org. Chem. 2010, 6, 810–822, doi:10.3762/bjoc.6.91

• -labeling of the bacterial lectin FimH. The target molecules 12 and 13 were selected after docking studies based on the structure of FimH and according to binding studies employing type 1-fimbriated E. coli. Photo-crosslinking was tested with the model peptide angiotensin II and the regiochemistry of the

Recent advances in carbocupration of α-heterosubstituted alkynes

• Ahmad Basheer and
• Ilan Marek

Beilstein J. Org. Chem. 2010, 6, No. 77, doi:10.3762/bjoc.6.77

• is opposite to that predicted on the basis of electronic or steric effects alone [6][7]. Therefore acetylenic ether 10 possessing an additional chelating group was prepared and the regiochemistry of the carbometalation investigated as shown in Scheme 6 [8]. The addition of various organocopper

• the organocopper by the oxygen of the THP completely reversed the regiochemistry of the carbocupration reaction [8]. Ethynyl carbamate is also an oxy-substituted acetylene (and therefore should lead to the branched product). However, the electron-withdrawing group properties of the carbamoyl group

• (branched/linear: 82/18), again showing that the chelation effect plays a major role in the regiochemistry of the carbometalation. The carbometalation of enantiomerically enriched cyclic ynamide 20 was recently used in a single-pot operation as a new entry to aldol products 21 possessing quaternary

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• regioisomers [22], and in the case of triazole 9, this regiochemistry was confirmed by 1H NOE spectra (see Supporting Information File 2). Conclusion In conclusion, routes to functionalized oxazolo[5,4-d]pyrimidines from 2-substituted 5-aminooxazole-4-carboxylic acid ethyl esters were developed, the key to

Solvent- controlled regioselective protection of allyl- 4,6-benzylidene glucopyranosides

• Kerry Ann Ness and
• Marie E. Migaud

Beilstein J. Org. Chem. 2007, 3, No. 26, doi:10.1186/1860-5397-3-26

• . Target partially protected sugar 1. Selective C-2 benzylation and confirmation of the regiochemistry through acetylation of the C-3 hydroxyl. a. BnBr, NaH, Bu4NI, THF, 80°C; b. Ac2O, DMAP, Py, MW, 5 mins, 80 W Reaction of 2 with alkylating, acylating and silylating reagents and products distribution

The use of silicon- based tethers for the Pauson- Khand reaction

• Adrian P. Dobbs,
• Ian J. Miller and
• Saša Martinović

Beilstein J. Org. Chem. 2007, 3, No. 21, doi:10.1186/1860-5397-3-21

• . Pagenkopf has shown that when the P-K cyclisation is carried out in 'wet' acetonitrile the cyclisation would proceed to give the cyclopentenones (Scheme 2).[8][9] The tethering strategy was not however successful in that although cyclisation gave the correct regiochemistry, the silicon tether is cleaved

The oxanorbornene approach to 3-hydroxy, 3,4-dihydroxy and 3,4,5-trihydroxy derivatives of 2-aminocyclohexanecarboxylic acid

• Ishmael B. Masesane,
• Andrei S. Batsanov,
• Judith A. K. Howard,
• Raju Mondal and
• Patrick G. Steel

Beilstein J. Org. Chem. 2006, 2, No. 9, doi:10.1186/1860-5397-2-9

• overcome the directing influence of the carbamate and deliver the epoxide to the opposite face of diene 5. Similarly, whilst the alternative regiochemistry in the epoxide ring opening product could be achieved exploiting neighbouring group participation by the NBoc group to afford the cyclic carbamate 29